The invention relates to a fluid filter for filtering fluid media, and more particularly to a fluid filter having a spring-loaded closure element for closing a drain opening.
A conventional fluid filter of this kind is shown and described in DE 33 44 568 A1. The closure element is designed as a mushroom-shaped valve. A first elongate spring acts on a valve shaft so that the valve head seals off a drain opening. When the filter insert is changed, the elongate spring releases the valve shaft so that the valve head opens the drain opening. This opening process is favored by a second coil spring which urges the valve head into its open position.
The foregoing valve arrangement is comparatively costly since it requires two springs' and because in addition the coil spring together with the valve head and a shoulder that is circumferential and provided on the valve shaft are located in an additional part, a so-called intermediate housing.
A fluid filter is also shown and described in U.S. Pat. No. 3,317,046 in which a plurality of essentially rectilinear leaf springs are provided as filter bypass valves whose opening and/or closing behavior is determined, as in the case of a check valve, by the flow and pressure conditions.
A diaphragm spring is also shown and described in DE-AS 1 611 121, in which the spring is designed as an annular spring element.
EP 322 828 A1 teaches as a spring element an annular rubber disk as well as a coil or helical spring.
EP 213 889 A2 also shows a drain valve with a coil spring.
The filter inserts can have different dimensions, for example as a result of manufacturing tolerances, but especially also because insert materials are used that change during the operating life of the filter insert. For example, the filter insert can be composed in the form of a plurality of paper or cardboard disks that collapse after being softened by the medium to be filtered, and thus shorten the length of the filter insert.
Especially in the case of such filter inserts with variable dimensions, there is the problem of ensuring reliable sealing of the drain opening during operation and to permit automatic opening of the drain opening provided in the filter housing when changing the filter insert.
One object of the invention is to improve a fluid filter in such fashion that a length adjustment to the changing dimensions of the filter insert over a range that is as wide as possible can be achieved with manufacturing costs that are as low as possible.
This goal which forms the basis of the invention is achieved by the following teachings.